| 1. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Soffitta, Paolo, et al.
(författare)
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XIPE : the X-ray imaging polarimetry explorer
- 2013
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 36:3, s. 523-567
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Tidskriftsartikel (refereegranskat)abstract
- X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2-10 keV band in 10(5) s for pointed observations, and 0.6 % for an X10 class solar flare in the 15-35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin x 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 mu s. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut fur extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.
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| 3. |
- Alcantara-Avila, Francisco, et al.
(författare)
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Validation of symmetry-induced high moment velocity and temperature scaling laws in a turbulent channel flow
- 2024
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Ingår i: Physical review. E. - : American Physical Society (APS). - 2470-0045 .- 2470-0053. ; 109:2
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Tidskriftsartikel (refereegranskat)abstract
- The symmetry -based turbulence theory has been used to derive new scaling laws for the streamwise velocity and temperature moments of arbitrary order. For this, it has been applied to an incompressible turbulent channel flow driven by a pressure gradient with a passive scalar equation coupled in. To derive the scaling laws, symmetries of the classical Navier-Stokes and the thermal energy equations have been used together with statistical symmetries, i.e., the statistical scaling and translation symmetries of the multipoint moment equations. Specifically, the multipoint moments are built on the instantaneous velocity and temperature fields other than in the classical approach, where moments are based on the fluctuations of these fields. With this instantaneous approach, a linear system of multipoint correlation equations has been obtained, which greatly simplifies the symmetry analysis. The scaling laws have been derived in the limit of zero viscosity and heat conduction, i.e., Ret -> infinity and Pr > 1, and they apply in the center of the channel, i.e., they represent a generalization of the deficit law, thus extending the work of Oberlack et al. [Phys. Rev. Lett. 128, 024502 (2022)]. The scaling laws are all power laws, with the exponent of the high moments all depending exclusively on those of the first and second moments. To validate the new scaling laws, the data from a large number of direct numerical simulations (DNS) for different Reynolds and Prandtl numbers have been used. The results show a very high accuracy of the scaling laws to represent the DNS data. The statistical scaling symmetry of the multipoint moment equations, which characterizes intermittency, has been the key to the new results since it generates a constant in the exponent of the final scaling law. Most important, since this constant is independent of the order of the moments, it clearly indicates anomalous scaling.
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| 4. |
- Alimena, Juliette, et al.
(författare)
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Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider
- 2020
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 47:9
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Tidskriftsartikel (refereegranskat)abstract
- Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments-as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER-to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.
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| 5. |
- Mialon, Bruno, et al.
(författare)
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Validation of numerical prediction of dynamic derivatives : The DLR-F12 and the Transcruiser test cases
- 2011
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Ingår i: Progress in Aerospace Sciences. - : Elsevier BV. - 0376-0421 .- 1873-1724. ; 47:8, s. 674-694
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Forskningsöversikt (refereegranskat)abstract
- The dynamic derivatives are widely used in linear aerodynamic models in order to determine the flying qualities of an aircraft: the ability to predict them reliably, quickly and sufficiently early in the design process is vital in order to avoid late and costly component redesigns. This paper describes experimental and computational research dealing with the determination of dynamic derivatives carried out within the FP6 European project SimSAC. Numerical and experimental results are compared for two aircraft configurations: a generic civil transport aircraft, wing-fuselage-tail configuration called the DLR-F12 and a generic Transonic CRuiser, which is a canard configuration. Static and dynamic wind tunnel tests have been carried out for both configurations and are briefly described within this paper. The data generated for both the DLR-F12 and TCR configurations include force and pressure coefficients obtained during small amplitude pitch, roll and yaw oscillations while the data for the TCR configuration also include large amplitude oscillations, in order to investigate the dynamic effects on nonlinear aerodynamic characteristics. In addition, dynamic derivatives have been determined for both configurations with a large panel of tools, from linear aerodynamic (Vortex Lattice Methods) to CFD. This work confirms that an increase in fidelity level enables the dynamic derivatives to be calculated more accurately. Linear aerodynamics tools are shown to give satisfactory results but are very sensitive to the geometry/mesh input data. Although all the quasi-steady CFD approaches give comparable results (robustness) for steady dynamic derivatives, they do not allow the prediction of unsteady components for the dynamic derivatives (angular derivatives with respect to time): this can be done with either a fully unsteady approach i.e. with a time-marching scheme or with frequency domain solvers, both of which provide comparable results for the DLR-F12 test case. As far as the canard configuration is concerned, strong limitations for the linear aerodynamic tools are observed. A key aspect of this work are the acceleration techniques developed for CFD methods, which allow the computational time to be dramatically reduced while providing comparable results.
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| 6. |
- Nordström, Henrik, et al.
(författare)
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Strategies for Continuous Balancing in Future Power Systems with High Wind and Solar Shares
- 2023
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 16:14
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Forskningsöversikt (refereegranskat)abstract
- The use of wind power has grown strongly in recent years and is expected to continue to increase in the coming decades. Solar power is also expected to increase significantly. In a power system, a continuous balance is maintained between total production and demand. This balancing is currently mainly managed with conventional power plants, but with larger amounts of wind and solar power, other sources will also be needed. Interesting possibilities include continuous control of wind and solar power, battery storage, electric vehicles, hydrogen production, and other demand resources with flexibility potential. The aim of this article is to describe and compare the different challenges and future possibilities in six systems concerning how to keep a continuous balance in the future with significantly larger amounts of variable renewable power production. A realistic understanding of how these systems plan to handle continuous balancing is central to effectively develop a carbon-dioxide-free electricity system of the future. The systems included in the overview are the Nordic synchronous area, the island of Ireland, the Iberian Peninsula, Texas (ERCOT), the central European system, and Great Britain.
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| 7. |
- Rivas-Gomez, Sergio
(författare)
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High-Performance I/O Programming Models for Exascale Computing
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The success of the exascale supercomputer is largely dependent on novel breakthroughs that overcome the increasing demands for high-performance I/O on HPC. Scientists are aggressively taking advantage of the available compute power of petascale supercomputers to run larger scale and higher-fidelity simulations. At the same time, data-intensive workloads have recently become dominant as well. Such use-cases inherently pose additional stress into the I/O subsystem, mostly due to the elevated number of I/O transactions.As a consequence, three critical challenges arise that are of paramount importance at exascale. First, while the concurrency of next-generation supercomputers is expected to increase up to 1000x, the bandwidth and access latency of the I/O subsystem is projected to remain roughly constant in comparison. Storage is, therefore, on the verge of becoming a serious bottleneck. Second, despite upcoming supercomputers expected to integrate emerging non-volatile memory technologies to compensate for some of these limitations, existing programming models and interfaces (e.g., MPI-IO) might not provide any clear technical advantage when targeting distributed intra-node storage, let alone byte-addressable persistent memories. And third, even though compute nodes becoming heterogeneous can provide benefits in terms of performance and thermal dissipation, this technological transformation implicitly increases the programming complexity. Hence, making it difficult for scientific applications to take advantage of these developments.In this thesis, we explore how programming models and interfaces must evolve to address the aforementioned challenges. We present MPI storage windows, a novel concept that proposes utilizing the MPI one-sided communication model and MPI windows as a unified interface to program memory and storage. We then demonstrate how MPI one-sided can provide benefits on data analytics frameworks following a decoupled strategy, while integrating seamless fault-tolerance and out-of-core execution. Furthermore, we introduce persistent coarrays to enable transparent resiliency in Coarray Fortran, supporting the "failed images" feature recently introduced into the standard. Finally, we propose a global memory abstraction layer, inspired by the memory-mapped I/O mechanism of the OS, to expose different storage technologies using conventional memory operations.The outcomes from these contributions are expected to have a considerable impact in a wide-variety of scientific applications on HPC, both in current and next-generation supercomputers.
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| 8. |
- Villarroel-Schneider, Johnny, et al.
(författare)
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Open-source model applied for techno-economic optimization of a hybrid solar PV biogas-based polygeneration plant : The case of a dairy farmers’ association in central Bolivia
- 2023
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 291
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Tidskriftsartikel (refereegranskat)abstract
- Proper sizing of energy systems is a key aspect that allows avoiding overestimated installation costs or failures in operation and dispatch. However, most of the available sizing tools focus on systems dedicated only to electrical loads, omitting combined energy systems with simultaneous supply of various thermal demands. This study presents an adaptation of an existing open access techno-economic optimization model for broadening the design tool for small-scale energy systems supplying both, electrical and thermal needs. For this, a new typology of an energy system was proposed considering the use of biogas, solar energy and adding thermal components. This was followed by modifying the model framework, constraints equations and objective function, which is the net present cost of the system. Once the design tool was verified a model was constructed to analyse the feasibility of a polygeneration plant for an association of 30 small dairy farms. The developed model was able to optimize the sizing of the main system components for different proposed scenarios, encompassing supply of electricity, refrigeration, biogas for cooking and fertilizers. For the selected application it was found that the aggregated cost of producing electricity and heat ranges from 0.044 to 0.070 USD/kWh; the penetration of solar energy can reach up to 32%; while the annual potential savings of CO2 emissions of applying the solution ranges from 109 to 127 ton of CO2.
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| 9. |
- Villarroel-Schneider, Johnny, et al.
(författare)
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Open-source model applied for techno-economic optimization of a hybrid solarPV biogas-based polygeneration plant: the case of a dairy farmers’ associationin central Bolivia
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Proper sizing of energy systems is a key aspect that allows avoiding overestimated installationcosts or failures in operation and dispatch. Most of the available sizing tools focus on systemsdedicated only to electrical loads, omitting combined energy systems with simultaneous supplyof various thermal demands. This study presents an adaptation of an existing techno-economicoptimization model for broadening the design tool for small-scale energy systems supplyingboth electrical and thermal needs. For this, a new typology of the energy system was proposedadding components such as a combustor and a combined heat and power generator. Thenmodifications were made to the model framework (constraints, parameters, variables andobjective function). The developed model was applied to a polygeneration plant for anassociation of 30 small dairy farmers, where biogas is proposed to be produced to cover thedemand for cooking gas and mainly for fuelling the plant that supplies electricity, refrigerationfor milk (by using absorption refrigeration technology) and heat for drying organic fertilizersthat result from biogas production. In addition, the use of solar PV panels and batteries isconsidered. Different scenarios for analysing and validating the model were proposed; thebase scenario allows the operation of all the system components, generating surpluses ofelectricity (for selling), heat (for other uses) and biogas. The aggregated cost of producingelectricity and heat ranges from 0.043 to 0.068 USD/kWh; the penetration of solar energyranges from 27 to 36%, while the potential savings of CO2 emissions of applying the proposedpolygeneration system ranges from 109 to 131 ton of CO2 per year.
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